David Shaw

Wind River Canopy Crane Research Facility, UW.

SUMMARY OF DATASET ON DWARF MISTLETOE INFECTIONS IN TREE CROWNS OF WESTERN HEMLOCK AND TRUE FIRS.

The WRCCRF and Jiquan Chen (Univ of Toledo) have installed a 12 ha stem-mapped plot in the T.T. Munger Research Natural Area, Wind River Experimental Forest, Gifford Pinchot National Forest, in SW Washington State. The stand is an old-growth (~500 yr) Douglas-fir/western hemlock stand. The plot includes the Wind River Canopy Crane (http://depts.washington.edu/wrccrf).

As part of the general scientific use of this plot, I (and collaborators) have been investigating the ecology of hemlock dwarf mistletoe (Arceuthobium tsugense), a hemi-parasitic plant that infects western hemlock, pacific silver fir, noble fir, and grand fir. The true firs are considered occasional hosts, whereas the western hemlock is the primary host.

Some background on dwarf mistletoe.

Hemlock dwarf mistletoe is a vascular plant that has explosively discharged seed. The seed is "shot" from the female plant up to about 15 m. The seed is sticky, and adheres to whatever it lands on. If the seed is lucky, it will land on foliage. When it rains, the seed slides down the needle and attaches at the needle base. A haustorium develops and the plant ramifies through the bark, only young branchlets can be infected. The plant forms a localized infection, perhaps not exceeding 50 cm lateral length, and eventually causes deformation and multiple branching of the infected stem. These infections are called "witches brooms" due to the characteristic broomy shape. The ecology of dwarf mistletoe is related to how it spreads, which is controlled by a number of factors, including stand structure, host -- non-host spatial patterns, stand density/spacing, and topography. Birds may passively aid spread of seed, but this mistletoe does not depend on vertebrates, as do most other mistletoes. Once established in a tree crown, a process called "intensification" takes over where the plants multiply within the crown and cause the tree to become overwhelmed with large numbers of infections, creating a tree which may be entirely witches brooms. The structure of the tree is quite different from an uninfected tree.

Hemlock dwarf mistletoe has been studied most intensively in the coastal rain forests where western hemlock is the primary successional species. Our knowledge of the ecology of hemlock dwarf mistletoe in the Douglas-fir forests of the Cascade Mts, where western hemlock is a secondary successional species is mostly anecdotal. The purpose of this study is to gain an appreciation of the spatial patterns of hemlock dwarf mistletoe in an old-growth Douglas-fir/western hemlock forest. We are interested in what factors are important in controlling the spread of the mistletoe in an old-growth forest, and specifically how our general knowledge of hemlock dwarf mistletoe applies to old growth in the Cascade Mts.

The traditional method of surveying dwarf mistletoe in western conifers involves a simple system called the Hawksworth 6 Class Dwarf Mistletoe Rating System (DMR). An individual tree crown is divided into thirds, vertically. Each third is assigned a number, from 0-2. 0 = no mistletoe present. 1 = less than 50% of the branches have infections. 2 = more than 50% of the branches in that third have infections. You then sum each third. Total tree is rated: 0 - 6.

The nice thing about this system is that crown thirds are separated and you can determine whether patterns exist. The negative aspect of this relates to the broad, brush stroke estimates of infection, and not a lot of detail is given within any one tree crown.

We surveyed all the trees on our 12 ha stem mapped plot, and assigned DMR numbers to all hemlock and true firs. The map allows us to determine the general spatial pattern of the infected trees across the site. With some element of vertical patterns in infected crowns.

DATASETS:

Two datasets are provided as excel spreadsheets.
1. 12 ha_arts.xls
2. Snags2001.xls

1. 12 ha_arts.xls

Arts = Arceuthobium tsugense, hemlock dwarf mistletoe.

This spreadsheet contains the entire live tree dataset, and for Abies and TSHE, the DMRs. Measured in 1999.

Individual folders are given for:
Notes.
Abies: Abam: Abies amabilis (pacific silver fir), A. procera (noble fir), A. grandis (grand fir).
Psme: Pseudotsuga menziesii (Douglas-fir)
Tabr: Taxus brevifolia (Pacific yew)
Thpl: Thuja plicata (western redcedar)
Tshe: Tsuga heterophylla (western hemlock)

Column Headings:

Tag. Tree number.
Species. 4 letter code, see above.
DBH. Diameter (cm) taken at 1.3 m.
Height. Height (m) to top of live crown, estimated based on regression.
L. Crown length, estimated based on regression.
MaxR. Maximum crown radius, estimated based on regression.
X. West-to-east distance (m) from plot origin.
Y. South-to-north distance (m) from X.
Z. Elevation (m).
L. Abies and TSHE lower crown third DMR, 0=no infection, 1 = less than 50% branches infected, 2 = more than 50% of the branches in that third infected.
M. Abies and TSHE middle crown third DMR, 0=no infection, 1 = less than 50% branches infected, 2 = more than 50% of the branches in that third infected.
U. Abies and TSHE upper crown third DMR, 0=no infection, 1 = less than 50% branches infected, 2 = more than 50% of the branches in that third infected.
T. Abies and TSHE total tree crown DMR, the sum of L, M, U for an individual tree. 0 = no infection, 6 = entire crown fully infected.

2. Snags2001.xls
This dataset is only standing dead trees (1999). It may be important for this study for two reasons. Are there aggregates of TSHE mortality we could associate with mistletoe? And does the pattern of non-hosts help explain the infections patterns on the plot?

Column headings:
Species. 4 letter species codes. See above.
Tag. Assigned tree numbers.
DBH. Diameter (cm) at 1.3 m, of snag in 1999.
Height. Measured height (m) of the snag.
X. West-to-east distance (m) from plot origin.
Y. South-to-north distance (m) from X.